someone really needs to buy 2 tomei's and mod it so it is true dual. that thing sounds awesome. props on bringing the db meter to try to show comparison lol.

dark:
tunes are expensive so it is probably best to wait until you have all the mods you plan on doing and then get a tune. test pipes and hfc always have the possibility of throwing a CEL, but depending on the ones you bought they might have a built in "fouler" where the senor is further away and likely wont throw a CEL. I had kinetix HFC and now have ART pipes and neither gave me a CEL. If you do have inspection you will not pass emissions with test pipes unless they fudge the paperwork for you :).